Magnetic bubble memories are well known in the art. A variety of detectors for bubbles also is known. Permalloy magnetoresistive detectors, for example, have been employed in commercially available bubble memories for bubble detection. One popular version of such a detector is disclosed in A. H. Bobeck, U.S. Pat. No. 3,810,132, issued May 7, 1974. That patent discloses an expander-detector arrangement operative to expand a bubble laterally with respect to the path of bubble propagation, to detect the expanded bubble, and to eliminate the detected bubble by movement to a guardrail. The guardrail structure and operation is shown in A. H. Bobeck, U.S. Pat. No. 3,729,726, issued Apr. 24, 1973. The latter patent also shows the organization of a bubble memory for operating in a major-minor mode. The major-minor organization for bubble memories was first disclosed in P. I. Bonyhard et al., U.S. Pat. No. 3,618,054, issued Nov. 2, 1971.
A bubble memory organized in a major-minor mode employs a plurality of closed minor loops in which bubbles circulate in response to a magnetic field reorienting in the plane of bubble movement. A major loop is formed adjacent the ends of the minor loop and includes a bubble generator and detector. Bubble transfer ports or replicate ports are formed between the major loop and the minor loops and are operative to move a bubble pattern to or from the minor loops on command as is now well understood.
We are concerned with the detector for bubbles and direct our attention primarily to a detector for an organization in which the major path is a loop operative to return bubbles to transfer ports at which they were first transferred from the minor loops. Such a loop arrangement permits the previously transferred (out) bubble pattern to be transferred (in) to vacancies in the minor loops created upon transfer out. A bubble memory including a major loop of this type conveniently employs an NDRO detector. An NDRO expander-detector employing permalloy is shown in A. H. Bobeck et al., U.S. Pat. No. 3,702,995, issued Nov. 14, 1972. Such a detector is employed within the major loop and is operative first to expand a bubble for detection and thereafter to contract the expanded bubble to its original size for continued movement in the major loop.
Permalloy expander-detectors have found commercial acceptance primarily because bubble propagation patterns also have been made of permalloy and the detector can be formed simultaneously with the propagation pattern as taught in W. Strauss, U.S. Pat. No. 3,609,720, issued Sept. 28, 1971. For nonpermalloy bubble memories, bubble expander-detectors can be made as well with electrical conductor patterns as taught in R. F. Fischer, U.S. Pat. No. 3,564,518, issued Feb. 16, 1971, because in such cases no processing advantage is gained by using permalloy detector arrangements. p Ion-implanted bubble memories also are well known. Such memories are first disclosed in M. Dixon et al., U.S. Pat. No. 3,792,452, issued Feb. 12, 1974. Ion-implanted memories also are organized in a major-minor mode. But a commercially suitable NDRO detector for ion-implanted bubble memories does not exist presently. The permalloy expander-detector described above cannot be used at present because of an incompatibility between a uniform ion implant required to suppress hard bubbles in a permalloy circuit (i.e., the expander-detector) and the uniform ion implant required to suppress hard bubbles in ion-implanted circuits. Further, the permalloy expander-detector requires entry from a permalloy track in turn requiring an ion-implanted to permalloy transition which is not available at present.
Conductor driven expander-detectors have been used experimentally to stretch a bubble laterally with respect to an originating path to couple a detector element arranged perpendicular to the path. But this type of detector has had deficiencies also. Particularly, with ion-implanted bubble memories, bubbles fail to remain in the originating path when destretched from the detector element. The problem addressed by this invention thus is the failure of ion-implanted magnetic bubble memories attributed to destretching of stretched bubbles for detection by an NDRO detector.